1. Field of the Invention
The present invention relates to a means and method for transmitting and receiving ultrasonic energy, and in particular, one which allows the use of a single ultrasonic transducer in a pulse/echo mode to generate and receive unipolar ultrasonic pulses over a wide frequency bandwidth.
2. Problems in the Art
Ultrasonic interrogation is a widely used and promising technique of nondestructive evaluation. Nondestructive evaluation allows analysis of the interior of materials or structures without physically opening up or breaking into the interior. The advantages of this are obvious.
It has been firmly established that ultrasound can be propagated into a material and that its returning echoes will contain information about the structure of the interior of the material. For example, ultrasonic waves directed into a solid, generally homogeneous material, should result in reflected echoes which are unperturbed. If, however, the material contain cracks, voids, discontinuities, or such things, the reflected echoes should give an indication of the existence of these types of things. Major problems exist, however, in obtaining reliable and pertinent information from the echoes, and interpreting the echoes.
A co-pending, co-owned application filed Feb. 8, 1990, by inventors Thompson and Hsu, entitled MEANS AND METHOD OF TRANSMITTING AND RECEIVING BROADBAND, UNIPOLAR ULTRASONIC PULSES FOR ULTRASONIC INSPECTION, (which is a continuation application from Ser. No. 181,094 filed Apr. 13, 1988) discusses in some detail the differences in the types of ultrasonic pulses that are used in ultrasonic nondestructive evaluation. It also discusses why what are called "unipolar pulses" are believed to be better than "bipolar pulses" in many cases of ultrasonic non-destructive inspection and evaluation.
The above referenced application discusses the significant problems encountered in generating and receiving unipolar ultrasonic pulses. It discloses one structure and method for doing so. Circuitry was used incorporating two what will be called "passive" switching elements to "switch" the circuitry between the transmit (or pulse) and the receive (or echo) portions of each cycle. These passive switches also ensure appropriate impedances in the circuit to maintain the unipolar nature of the ultrasonic pulses from their generation to their reception.
It has been found that there is room for improvement with regard to this design. For example, it required utilization of and connection to a discrete square wave generator device, which in actuality itself contained a switch which was needed to maintain the unipolar nature of the pulses. It would be advantageous to be able to incorporate the square wave generator into the circuitry of an instrument to avoid the necessity of a separate square wave generator.
Additionally, there is a need for a unitary instrument that has a quicker transition time between transmit and receive states and maintains or improves upon the excellent bandwidth and time resolution of the co-pending application.
While the device described in the above mentioned application does present a viable way of generating and receiving unipolar ultrasonic pulses, there is a need in the art for improvement of the procedure and instrument used for the procedure. It is therefore a primary object of the present invention to provide an ultrasonic unipolar pulse/echo instrument and method which improves over or solves the problems and deficiencies in the art.
Another object of the present invention is to provide an instrument and method as above described which maintains the unipolar nature of the ultrasonic pulses in both the transmit (pulse) and receive (echo) portions of each cycle.
A still further object of the present invention is to provide an instrument and method as above described which has an improved bandwidth without sacrificing time resolution.
A still further object of the present invention is to provide and instrument and method as above described which results in improved return echoes of the unipolar pulses.
A further object of the present invention is to provide an instrument and method which utilizes active switches to accomplish improved unipolar pulse/echo operation.
Another object of the present invention is to provide an instrument and method as above described which results in improved output voltage during transmission and fast transition between transmit and receive operations.
Another object of the present invention is to provide an instrument and method as above described which can be operated from a single unitary instrument.
Another object of the present invention is to provide an instrument and method as above described which is reliable, efficient, and economical.
These and other objects, features, and advantages of the present invention will become apparent with reference to the accompanying specification and claims.